docs: def process_message(self, actor, body, message):
          """Process actor message depending depending on the the worker settings.
  
          If greenlets are enabled in the worker, the actor message is processed
          in a greenlet from the greenlet pool,
          Otherwise, the message is processed by the same thread.
          The method is invoked from the callback `cell.actors.Actor.on_message`
           upon receiving of a message.
  
          :keyword actor: instance of :class:`Actor` or its derivative.
          The actor instance to process the message.
  
          For the full list of arguments see
          :meth:`cell.actors.Actor._on_message`.
  
          """
          if actor is not self and self.is_green():
              self.pool.spawn_n(actor._on_message, body, message)
          else:
              if not self.is_green() and message.properties.get('reply_to'):
                  warn('Starting a blocking call (%s) on actor (%s) '
                       'when greenlets are disabled.',
                       itemgetter('method')(body), actor.__class__)
              actor._on_message(body, message)